Access points with selective communication rate and scheduling control and related methods for wireless local area networks (WLANs)

ABSTRACT

The present invention is directed to methods and wireless communication devices that are configured to enhance communication capacity in a wireless network. In one aspect of the invention various scheduling processes and schedulers for the transmissions of data packets are disclosed. In another aspect of the invention, the selection of appropriate transmission rates to advertise by a common unit which provides wireless service to different types of wireless transmit receive units (WTRUs) is addressed.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims priority from U.S. Patent Application No.60/517,833, filed Nov. 6, 2003 and U.S. Patent Application No.60/525,963, filed Dec. 1, 2003, which are incorporated by reference asif fully set forth.

FIELD OF INVENTION

This application relates to apparatus and methods for wirelesscommunication and in particular the control of data rates and schedulingof wireless communications for wireless local area networks (WLANs),particularly those compliant with one or more of the family of standardsknown as 802.11.

BACKGROUND OF THE INVENTION

Wireless communication systems are well known in the art. Generally,such systems comprise communication stations, which transmit and receivewireless communication signals between each other. Depending upon thetype of system, communication stations typically are one of two types:base stations or wireless transmit/receive units (WTRUs), which includemobile units.

The term base station as used herein includes, but is not limited to, abase station, Node B, site controller, access point or other interfacingdevice in a wireless environment that provides WTRUs with wirelessaccess to a network with which the base station is associated.

The term WTRU as used herein includes, but is not limited to, a userequipment, mobile station, fixed or mobile subscriber unit, pager, orany other type of device capable of operating in a wireless environment.WTRUs include personal communication devices, such as phones, videophones, and Internet ready phones that have network connections. Inaddition, WTRUs include portable personal computing devices, such asPDAs and notebook computers with wireless modems that have similarnetwork capabilities. WTRUs that are portable or can otherwise changelocation are referred to as mobile units. Generically, base stations arealso WTRUs.

Typically, a network of base stations is provided where each basestation is capable of conducting concurrent wireless communications withappropriately configured WTRUs. Some WTRUs are configured to conductwireless communications directly between each other, i.e., without beingrelayed through a network via a base station. This is commonly calledpeer-to-peer wireless communications. Where a WTRU is configured tocommunicate with other WTRUs it may itself be configured as and functionas a base station. WTRUs can be configured for use in multiple networkswith both network and peer-to-peer communications capabilities.

One type of wireless system, called a wireless local area network(WLAN), can be configured to conduct wireless communications with WTRUsequipped with WLAN modems that are also able to conduct peer-to-peercommunications with similarly equipped WTRUs. Currently, WLAN modems arebeing integrated into many traditional communicating and computingdevices by manufacturers. For example, cellular phones, personal digitalassistants, and laptop computers are being built with one or more WLANmodems.

A popular wireless local area network environment with one or more WLANbase stations, typically called access points (APs), is built accordingto the IEEE 802.11b standard. Access to these networks usually requiresuser authentication procedures. Protocols for such systems are presentlybeing standardized in the WLAN technology area. One such framework ofprotocols is the IEEE 802 family of standards.

The basic service set (BSS) is the basic building block of an IEEE802.11 WLAN and this consists of WTRUs typically referred to as stations(STAs). Basically, the set of STAs which can talk to each other can forma BSS. Multiple BSSs are interconnected through an architecturalcomponent, called a distribution system (DS), to form an extendedservice set (ESS). An access point (AP) is a station (STA) that providesaccess to the DS by providing DS services and generally allowsconcurrent access to the DS by multiple STAs.

The 802.11 standards allow multiple transmission rates (and dynamicswitching between rates) to be used to optimize throughput. The lowerrates have more robust modulation characteristics that allow greaterrange and/or better operation in noisy environments than the higherrates. The higher rates provide better throughput. It is an optimizationchallenge to always select the best (highest) possible rate for anygiven coverage and interference condition.

The currently specified rates of various versions of the 802.11 standardare set forth in Table 1 as follows:

TABLE 1 802.11 Standard Data Rates Standard Supported Rates (Mbps)802.11 (original) 1, 2 802.11a 6, 9, 12, 18, 24, 36, 48, 54 802.11b 1,2, 5.5, 11 802.11g 1, 2, 5.5, 6, 9, 11, 12, 18, 24, 36, 48, 54For 802.11g, the rates 6, 9, 12, 18, 24, 36, 48 and 54 Mbps useorthogonal frequency division modulation (OFDM). The choice of the ratecan affect performance in terms of system and user throughput, range andfairness.

Conventionally, each 802.11 device has a Rate Control algorithmimplemented in it that is controlled solely by that device.Specifically, uplink (UL) Rate Control in STAs and down link (DL) RateControl in APs. The algorithm for rate switching is not specified by thestandards. It is left up to the STA (and AP) implementation.

The inventors have recognized that each STA typically gets equalopportunity to send packet data. However, a packet sent at a lower ratetakes much longer than one sent at higher rate and where a WLAN has asingle shared channel, the lowest data rate will cause the capacity ofthe AP with which the STAs are communicating to be reduced.

Also, APs often must handle communications for multiple STAs. Thispresents a scheduling issue for the downlink transmissions for data tothe various STAs. The inventors have recognized that data queues may beadvantageously used by the APs based of on class of service incombination with the use of a priority system for releasing data fromthe respective queues for transmission.

In some instances, APs are configured to provide wireless services tomore than one type of STA. For example, devices compliant to the IEEE802.11g standard have become available. These devices operate in thesame channels as existing 802.11b devices, but operate at a higherthroughput rate. Systems operating under the 802.11g standard arepreferably configured such that both 802.11b and 802.11g STAs cancommunicate with an 802.11g AP, in order to allow coexistence withlegacy 802.11b systems.

As noted above, all 802.11 systems permit a choice of transmission ratesfor radio transmissions, but the rate to choose for a transmission isimplementation dependent. The obvious solution is to choose the ratethat maximizes throughput for a particular transmission. This impliesthat for the same signal strength and interference levels, 802.11g OFDMrates would always be chosen over 802.11b rates, assuming equivalentreceiver performance. However, as discussed below, the inventors haverecognized that this does not ensure fair access to the availablebandwidth for 802.11b devices. It is thus advantageous to providetransmission rates which take into account the distinctions in theoperating characteristics of 802.11b and 802.11g devices to more fairlyallocate transmission rates among the 802.11b and 802.11g devices.

SUMMARY

The present invention is directed to methods and wireless communicationdevices that are configured to enhance communication capacity in awireless network. In one aspect of the invention various schedulingprocesses and schedulers for the transmissions of data packets aredisclosed. In another aspect of the invention, the selection ofappropriate transmission rates to advertise by a common unit whichprovides wireless service to different types of wireless transmitreceive units (WTRUs) is addressed.

In one embodiment, a WTRU is provided for conducting wirelesscommunications with a plurality of other WTRUs that implements a processfor controlling transmission of wireless communication data to the otherWTRUs. The WTRU has a scheduler configured to queue data packets fortransmission to other WTRUs based on transmission rate. The schedulerselectively enables transmission of queued data packets fromtransmission rate assigned queues in successive turns based on anallocated time period for each queue turn such that a shortest timeperiod is allocated for data packets queued in a lowest data rate queueand a longest time period is allocated for data packets queued in ahighest data rate queue. Preferably, the scheduler is configured toallocate a time period for a given queue that is at least as long as thetime period allocated for each queue assigned for data packetsdesignated for transmission at a lower data rate than the data rateassigned to the given queue. Such a WTRU is advantageously configured asan Access Point (AP) for a 802.11 wireless local area network (WLAN).

Broadly, the WTRU's scheduler can be configured to selectively enablecommunication of data packets with other WTRUs in successive turns basedon an allocated time period for each turn such that a shortest timeperiod is allocated for data packets communicated at a lowest data rateand a longest time period is allocated for data packets communicated ata highest data rate. Preferably, the scheduler is configured to allocatetime periods for receiving data packets from other WTRUs such that eachother WTRU is provided a transmission time for its respective turn basedupon the transmission rate at which that WTRU is to transmit datapackets that is at least as long as the time period allocated for datapackets designated for transmission at a lower data rate than thetransmission rate at which that WTRU is to transmit data packets. Inaddition, the scheduler can be configured to queue data packets fortransmission to other WTRUs based on transmission rate and toselectively enable transmission of queued data packets from transmissionrate assigned queues in successive turns based on an allocated timeperiod for each queue turn such that a shortest time period is allocatedfor data packets queued in a lowest data rate queue and a longest timeperiod is allocated for data packets queued in a highest data ratequeue. In such case, the scheduler is preferably configured to allocatea time period for a given queue that is at least as long as the timeperiod allocated for each queue assigned for data packets designated fortransmission at a lower data rate than the data rate assigned to thegiven queue. Such a WTRU is advantageously configured as an Access Point(AP) for a 802.11 wireless local area network (WLAN).

Corresponding methods are provided for conducting wireless communicationof data between a wireless transmit/receive unit (WTRU) and a pluralityof other WTRUs and for controlling transmission of such communicationdata to the other WTRUs. Data packets are queued for transmission toother WTRUs based on transmission rate. The transmission of queued datapackets from transmission rate assigned queues is selectively enabled insuccessive turns based on an allocated time period for each queue turnsuch that a shortest time period is allocated for data packets queued ina lowest data rate queue and a longest time period is allocated for datapackets queued in a highest data rate queue. Preferably, a time periodis allocated for a given queue that is at least as long as the timeperiod allocated for each queue assigned for data packets designated fortransmission at a lower data rate than the data rate assigned to thegiven queue.

Broadly, the method entails selectively enabling communication of datapackets with other WTRUs in successive turns based on an allocated timeperiod for each turn such that a shortest time period is allocated fordata packets communicated at a lowest data rate and a longest timeperiod is allocated for data packets communicated at a highest datarate. Preferably, time periods are allocated for receiving data packetsfrom other WTRUs such that each other WTRU is provided a transmissiontime for its respective turn based upon the transmission rate at whichthat WTRU is to transmit data packets that is at least as long as thetime period allocated for data packets designated for transmission at alower data rate than the transmission rate at which that WTRU is totransmit data packets. Additionally, data packets can be queued fortransmission to other WTRUs based on transmission rate and then thetransmission of queued data packets is selectively enabled fromtransmission rate assigned queues in successive turns based on anallocated time period for each queue turn such that a shortest timeperiod is allocated for data packets queued in a lowest data rate queueand a longest time period is allocated for data packets queued in ahighest data rate queue. In such a case, a time period is preferablyallocated for a given queue that is at least as long as the time periodallocated for each queue assigned for data packets designated fortransmission at a lower data rate than the data rate assigned to thegiven queue.

In another embodiment, the WTRU's scheduler is configured to queue datapackets for transmission to other WTRUs based on selected criteria. Aqueue arrival time is identified with each queued data packet whereby ineach queue in which data packets are queued, a data packet is disposedat a head of the queue that has an identified earliest queue arrivaltime relative to the queue arrival time identified with other datapackets in the same queue. Preferably, the scheduler is furtherconfigured to selectively enable transmission of queued data packets byremoving a data packet for transmission processing from the head of oneof the queues based on a priority index calculated for each data packetconcurrently disposed at the head of one of the queues. The scheduler ispreferably configured to calculate the priority index of a data packetusing the queue arrival time identified with the data packet and a datatransmission rate associated with the data packet.

In one variation of such an embodiment, the scheduler is configured toqueue data packets based on data transmission rate identified with eachdata packet such that data packet queues are defined for different datarates. Where there are defined classes of service for data transmission,each identified with a data transmission rate, the scheduler ispreferably configured to queue data packets based on class of serviceidentified with each data packet such that data packet queues aredefined for each class of service.

In another variation of such an embodiment, the scheduler is configuredto queue data packets based on a destination WTRU identified with eachdata packet such that a data packet queue is defined for each differentdestination WTRU. In either case, the WTRU is advantageously configuredas an Access Point (AP) for a 802.11 wireless local area network (WLAN).

In implementation, the WTRU can include a memory device and anassociated processor. The memory device is preferably configured withselectively defined data packet transmission queues based on selecteddata packet characteristics. The processor is preferably configured toassociate a queue arrival time with successive data packets received fortransmission queuing and to store each data packet in connection withits queue arrival time in a respective queue based on the selected datapacket characteristics. As a result, in each queue in which data packetsare stored, a data packet is disposed at a head of the queue that has anidentified earliest queue arrival time relative to the queue arrivaltime identified with other data packets in the same queue. The processoris also preferably configured to selectively enable transmission ofqueued data packets by removing a data packet for transmissionprocessing from the head of one of the queues based on a priority indexcalculated for each data packet concurrently disposed at the head of oneof the queues. In such a case, the processor is preferably configured tocalculate the priority index of a data packet using the queue arrivaltime identified with the data packet and a data transmission rateassociated with the data packet.

In one variation of such an embodiment, the memory device is configuredsuch that data packet queues are defined for different data rates andthe processor is configured to store data packets in respective queuesbased on a data transmission rate identified with each data packet.Where there are defined classes of service for data transmission, eachidentified with a data transmission rate, the processor is preferablyconfigured to queue data packets based on class of service identifiedwith each data packet such that data packet queues are defined in thememory device for each class of service.

In another variation of such an embodiment, the memory device isconfigured such that data packet queues are defined for differentdestination WTRUs and the processor is configured to store data packetsin respective queues based on a destination WTRU identified with eachdata packet. In either case, the WTRU is advantageously configured as anAccess Point (AP) for a 802.11 wireless local area network (WLAN).

A corresponding method is provided that includes queuing data packetsfor transmission to other WTRUs based on selected criteria such that aqueue arrival time is identified with each queued data packet. As aresult, in each queue in which data packets are queued, a data packet isdisposed at a head of the queue that has an identified earliest queuearrival time relative to the queue arrival time identified with otherdata packets in the same queue. Transmission of queued data packets isthen selectively enabled by removing a data packet for transmissionprocessing from the head of one of the queues based on a priority indexcalculated for each data packet concurrently disposed at the head of oneof the queues. Preferably, the calculating of the priority index of adata packet uses the queue arrival time identified with the data packetand a data transmission rate associated with the data packet.

In another variation of such a method, data packets are queued based ondata transmission rate identified with each data packet such that datapacket queues are defined for different data rates. Where steps areperformed by an Access Point (AP) for a 802.11 wireless local areanetwork (WLAN) that has classes of service for data transmission, eachidentified with a data transmission rate, data packets are preferablyqueued based on class of service identified with each data packet suchthat data packet queues are defined for each class of service.

In another variation of such an embodiment, data packets are queuedbased on a destination WTRU identified with each data packet such that adata packet queue is defined for each different destination WTRU. Such amethod is advantageously performed by an Access Point (AP) for a 802.11wireless local area network (WLAN).

In another aspect of the invention, a method is provided for a wirelesstransmit/receive unit (WTRU) to conduct wireless communications with aplurality of other WTRUs that implements a process for advertisingavailable wireless communication data rates to the other WTRUs where theother WTRUs include a first type of WTRU capable of communicating atdata rates in a first defined set of rates and a second type of WTRUcapable of communicating at data rates in a second defined set of ratesthat include first type data rates that are useable by both the firstand second types of WTRUs and second type data rates that are useable bythe second type of WTRUs, but not the first type of WTRUs. A number m ofthe first type of WTRUs and a number n of the second type of WTRUswirelessly communicating with the rate advertising WTRU are determined.A quality of a radio link between the rate advertising WTRU and thefirst and second types of WTRUs with which it is communicating is alsodetermined. Then support of the second defined set of data rates isadvertised when m=0 or when the determined radio link quality lies at adesired level and n=0. The method can additionally include thedetermining of a quality of a radio link includes determining of a frameerror rate (FER) such that a desired level of link quality is determinedwhen the FER is below a predetermined threshold.

In addition or in the alternative, the method may include advertisingsupport of the second defined set of data rates when m≠0, n≠0 and all ofthe second type of WTRUs are communicating with the rate advertisingWTRU at second type data rates that are not useable by the first type ofWTRUs. Such methods are advantageously performed by an Access Point (AP)for a wireless local area network (WLAN) that is configured forcommunicating with 1, 2, 5.5, 6, 9, 11, 12, 18, 24, 36, 48 and 54 Mbpsdata rates where the first defined set of rates includes 1, 2, 5.5 and11 Mbps data rates and the second defined set of rates includes 1, 2,5.5, 6, 9, 11, 12, 18, 24, 36, 48 and 54 Mbps data rates. In such acase, the first type of data rates that are usable by the first andsecond types of WTRUs include 1, 2, 5.5 and 11 Mbps the second type ofdata rates that are not usable by the first type of WTRUs include 6, 9,12, 18, 24, 36, 48 and 54 Mbps. In such a case, the advertising supportof the second defined set of data rates is preferably performed when allof the second type of WTRUs that are communicating with the AP arecommunicating at data rates greater than 11 Mbps.

In addition or in the alternative, the method may also includeadvertising support of the second defined set of data rates when m≠0, atleast one of the second type of WTRUs is communicating with the rateadvertising WTRU at a first type data rate and m/n is greater than orequal to a predetermined WTRU ratio threshold. As a further addition oralternative, the method may also include advertising support of thefirst type of data rates and not the second type of data rates when m≠0,at least one of the second type of WTRUs is communicating with the rateadvertising WTRU at a first type data rate and m/n is less than apredetermined WTRU ratio threshold. Preferably, the advertising supportof the first type of data rates and not the second type of data ratesincludes advertising support of the first defined set of data rates andcommunications on unadvertised rates is disabled in the rate advertisingWTRU.

For implementation, a rate advertising WTRU is preferably provided thatis configured to conduct wireless communications with a plurality ofother WTRUs and to advertise available wireless communication data ratesto the other WTRUs where the other WTRUs include a first type of WTRUcapable of communicating at data rates in a first defined set of ratesand a second type of WTRU capable of communicating at data rates in asecond defined set of rates that include first type data rates that areuseable by both the first and second types of WTRUs and second type datarates that are useable by the second type of WTRUs, but not the firsttype of WTRUs. Preferably, such a WTRU has a receiving unit, a signalprocessing unit and a transmitting unit. The receiving unit ispreferably configured to determine a number m of the first type of WTRUsand a number n of the second type of WTRUs wirelessly communicating withthe rate advertising WTRU. The signal processing unit is preferablyconfigured to determine a quality of a radio link between the rateadvertising WTRU and the first and second types of WTRUs with which itis communicating. The transmitting unit is preferably configured toadvertise support of the second defined set of data rates when m=0 orwhen the determined radio link quality lies at a desired level and n=0.The signal processing unit can be configured to determine a quality of aradio link by determining of a frame error rate (FER) such that adesired level of link quality is determined when the FER is below apredetermined threshold.

As an alternative or in addition, the transmitting unit can beconfigured to advertise support of the second defined set of data rateswhen m≠0, n≠0 and all of the second type of WTRUs are communicating withthe rate advertising WTRU at second type data rates that are not useableby the first type of WTRUs.

Such WTRUs are advantageously configured to communicate at 1, 2, 5.5, 6,9, 11, 12, 18, 24, 36, 48 and 54 Mbps data rates as an Access Point (AP)for a wireless local area network (WLAN) where the first defined set ofrates includes 1, 2, 5.5 and 11 Mbps data rates and the second definedset of rates includes 1, 2, 5.5, 6, 9, 11, 12, 18, 24, 36, 48 and 54Mbps data rates where the first type of data rates that are usable bythe first and second types of WTRUs include 1, 2, 5.5 and 11 Mbps thesecond type of data rates that are not usable by the first type of WTRUsinclude 6, 9, 12, 18, 24, 36, 48 and 54 Mbps. In such case, thetransmitting unit is preferably configured to advertise support of thesecond defined set of data rates when all of the second type of WTRUsthat are communicating with the WTRU are communicating at data ratesgreater than 11 Mbps.

As a further alternative or addition, the transmitting unit can beconfigured to advertise support of the second defined set of data rateswhen m≠0, at least one of the second type of WTRUs is communicating withthe rate advertising WTRU at a first type data rate and m/n is greaterthan or equal to a predetermined WTRU ratio threshold. Also, thetransmitting unit can be configured to advertise support of the firsttype of data rates and not the second type of data rates when m≠0, atleast one of the second type of WTRUs is communicating with the rateadvertising WTRU at a first type data rate and m/n is less than apredetermined WTRU ratio threshold. In such case, the transmitting unitis preferably configured to advertise support of the first defined setof data rates and to disable communications on unadvertised rates whenm≠0, at least one of the second type of WTRUs is communicating with therate advertising WTRU at a first type data rate and m/n is less than thepredetermined WTRU ratio.

Other objects and advantages of the present invention will be apparentto persons skilled in the art from the following description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system overview diagram illustrating WLAN communication.

FIG. 2 is a schematic diagram of a queue system for a “Class ofService”-aware scheduler of an AP having queues allocated on a “Class ofService” basis.

FIG. 3 is a schematic diagram of a queue system for a “Class ofService”-unaware scheduler of an AP having queues allocated on a STAbasis.

FIG. 4 is a plot showing the effective throughput versus distance for afree space path loss model that compares 802.11b and 802.11g devices.

FIG. 5 is a diagram illustrating a WLAN comprised of 802.11b STAscommunicating with an 802.11b/802.11g compatible AP with an accompanyingexample of data transmission sequence.

FIG. 6 is a diagram illustrating a WLAN comprised of an 802.11b STA andan 802.11g STA communicating with an 802.11b/802.11g compatible AP withan accompanying example of data transmission sequence.

FIG. 7 is a flow diagram showing method steps for choosing bittransmission rate(s) based on the number of 802.11b and 802.11g STAs,the signal quality of these devices and fairness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described with reference to the drawing figureswherein like numerals represent like elements throughout. The terms basestation, Access Point (AP), Station (STA), WTRU, and mobile unit areused in their general sense as described above. The present inventionprovides a wireless radio access network having one or more networkedbase stations through which wireless access service is provided forWTRUs. The invention is particularly useful when used in conjunctionwith mobile units or mobile STAs, as they enter and/or travel throughthe respective areas of geographic coverage provided by respective basestations or other APs.

In accordance with the invention, WTRUs can be configured with apeer-to-peer mode of operation, preferably, by being equipped withwireless local area network (WLAN) modems to exchange informationdirectly between similarly equipped WTRUs. The WTRUs can have anintegrated or installed wireless WLAN device, such as 802.11(b),802.11(g), WiFi or Bluetooth compliant device, in order to communicatewith each other. However, the proposed invention is applicable in anywireless system.

Referring to FIG. 1, a WLAN is illustrated where WTRUs conduct wirelesscommunications via an Access Point (AP) 54 which can be connected withother network infrastructure such as a Network Management Station (NMS)16. The AP 54 is shown as conducting communications with WTRU 18, WTRU20, WTRU 22, WTRU 24, and WTRU 26. The communications are coordinatedand synchronized through the AP 54. Such a configuration is also calleda basic service set (BSS) within WLAN contexts.

Generally, the WLAN system supports WTRUs with different data rates. Insome cases an AP is configured to support multiple types of WTRUs, suchas 802.11(b) compliant WTRUs as well as 802.11(g) compliant WTRUs. Insuch a case the data rates available to the 802.11(g) compliant WTRUsare more numerous as reflected in the rate chart above.

Where the AP 54 is configured to support one type of WTRU, such as only802.11(a) compliant WTRUs, each WTRU gets an equal opportunity to sendcommunications such as packet data, but the rate used may be differentand can depend on a variety of factors which are typically related tothe quality of service (QoS) of the particular WTRU-AP communication. Adata packet sent at a lower rate takes much longer than one sent at ahigher rate. For a WLAN having a single shared channel for such packetdata, the lowest data rate used for communicating a data packet controlsand causes a limitation to the capacity of the AP.

According to the teachings of the present invention, the AP preferablyschedules packet data based on the time it takes to send the packet.Using as limits the maximum allowed time in queue and required delay QoSfor the particular service, the amount of time allocated for variousrates is selectively decided in order to optimize the capacity of thenetwork. To do this, the AP preferably schedules the data packets fordifferent STAs based on the time it takes to send packets of a certainsize, not on the number of packets sent. In order to optimize theoverall AP capacity/throughput, more time is allocated to higher datarate services and less time to lower rate services. Accordingly, thissolves a current problem of lower overall AP throughput due to singlelow rate device.

For example, with reference to FIG. 1, the WTRUs and AP 54 can beconfigured to operate under the 802.11(a) standard. The AP would thendecide how to permit packets to be sent for the following relative timesdependent on rate as reflected in Table 2, where T₁ represents theshortest maximum time interval for the slowest rate which in the case of802.11a is currently 6 Mpbs.

TABLE 2 Example of Packet Data Time Allocation Per Rate For A 802.11aSystem Rate (Mbps) 6 9 12 18 24 36 48 54 Time T₁ 1.5 T₁ 2 T₁ 3 T₁ 4 T₁ 5T₁ 6 T₁ 6 T₁ Allotted

WTRU 18 may have data packets to communicate at a rate of 48 Mbps; WTRU20 may have data packets to communicate at a rate of 12 Mbps; WTRU 22may have data packets to communicate at a rate of 36 Mbps; WTRU 24 mayhave data packets to communicate at a rate of 6 Mbps; WTRU 26 may havedata packets to communicate at a rate of 54 Mbps. In such a case, WTRU18 would be allocated 3T₁ to communicate data packets at its turn; WTRU20 would be allocated 2T₁ to communicate data packets at its turn; WTRU22 would be allocated 5T₁ to communicate data packets at its turn; WTRU24 would be allocated 1T₁ to communicate data packets at its turn; WTRU26 would be allocated 6T₁ to communicate data packets at its turn.

If, for example, WTRU 18 only used 2T₁ to communicate its data packetsat its turn, preferably the next WTRU would commence its turn forsending data packets. If, however, WTRU 18 required 5T₁ to communicateits data packets, it would only be able to send a portion of thosepackets at a first turn, and would need to wait until its next turnbefore sending its remaining data packets.

One implementation of the invention for an AP is to have a memoryconfigured with queues for packet data to be transmitted at each of thevarious rates. The AP can then transmit queued data packets torespective WTRUs by simply taking queued packets from each queue in apredefined sequence, where the number of packets transmitted for eachqueue's turn is based on the time allocated for the data rate associatedwith the queue.

For example for an AP serving 802.11(a) WTRUs, eight queues, one foreach of the eight data rates can be provided. An AP scheduler operatingin conjunction would repeatedly access each queue in a predefinedsequence such as the lowest to highest rate queue, i.e. 6 Mbps queue, 9Mbps queue, 12 Mbps queue, 18 Mbps queue, 24 Mbps queue, 36 Mbps queue,48 Mbps queue, 54 Mbps queue. The access would be preferably configuredto last up to the allotted time indicated for the particular servicerate, i.e., T₁ for the 6 Mbps queue and 4 T₁ for the 24 Mbps queue forthe example provided in the table above. If, only 2T₁ were required tocommunicate the data packets in the 24 Mbps queue at its turn,preferably the next turn for sending data packets from the 36 Mbps queuewould commence without waiting for 4 T₁ to expire. If, however, 5T₁ wererequired to communicate the data packets in the 24 Mbps queue at itsturn, the later queued packets would remain in the 24 Mbps queue untilits next turn before they were sent. Where no packets are queued in aparticular queue at its turn, that queue is preferably skipped for thatturn.

Preferably, the scheduler is configured to limit the maximum allowedtime in the queue permitted for QoS criteria for each respectiveservice. However, the amount of time allocated for various rates can bevaried to optimize the capacity of the network based on load or othercriteria. For example, tracking the number of packets residing in eachqueue may be used to increase or decrease queue allocation times foreach series of queue access turns. Accordingly, if tracking reflected nocurrent packets in the 24 Mbps, 36 Mbps and 48 Mbps queues, thescheduler may be configured to then decide to double the access timeallocated to each other queue for that series of turns.

Optimizing the overall AP Capacity/throughput by allocating more time tohigher data rate services, by itself, can result in relatively largesystem and STA delays. Accordingly, in lieu of configuring the schedulerof an AP data packet transmitter to select packets from queues in apredefined queue access series, a scheduler may be provided thatschedules packets based on a priority index value determined for queuedpackets.

Queue and scheduler configurations can be varied to accommodatedifferent system designs and options. For example, the AP may beselectively configured depending upon whether or not the servicerequirements for data packets to be transmitted to STAs are known to theAP. In each case, the objective is for the scheduler to be configured inan attempt to optimize system throughput. Where possible, the schedulerpreferably is configured with consideration of delay requirements fordifferent services. Two examples are provided below for the case where ascheduler 30 is aware of Class-of-Service (CoS) information as reflectedin FIG. 2 and the case where a scheduler 40 is unaware ofClass-of-Service information as reflected in FIG. 3. In general, therespective schedulers 30, 40 comprise a respective memory devicerepresented by the boxes and data blocks in FIGS. 2 and 3 and anassociated processing device represented by the heavy arrows in FIGS. 2and 3. For an 802.11 type of AP, the scheduler 30, 40 is typicallysituated to selectively release data packets to a MAC buffer fortransmission processing, having received the data packets from higherlayers of communication processing.

With reference to FIG. 2, pre-classified traffic, i.e. data packets thatare already classified according to their respective servicerequirements (e.g. CoS settings within IEEE 802.1D, IEE 802.1P or802.1Q, etc), arrives at a transmission scheduler component 30 of an AP.In this case, the scheduler preferably has a transmission queue that isstructured with a selected number of individual queues, each designatedfor data packets of a different type of service. For an example CoSaware case, the memory device is preferably configured with fourindividual queues 32 a-32 d to buffer data packets for voice, video,interactive data and low priority data, respectively. In FIG. 2, datapackets are illustrated as appropriately distributed in each of thequeues, the respective shading of the data packets representing its CoS.

Data packets arrive via a processing input 31 and are time stamped withan arrival time by a time stamping component 33 of the processingdevice. An input buffer 34 is preferably provided to the time stampingelement 33. A distribution element 35 of the processing device queueseach time stamped data packet into the tail of one of respectivepriority queues 32 a-32 d according to its service requirements. A voicedata packet 36 is illustrated as being queued into the tail of the voiceservice queue 32 a by distribution element 35.

The scheduler 30 contains a calculating component 37 that calculates aPriority Index of each packet at the head of each queue 32 a-32 d. Adistribution output 39 of the scheduler 30, then sends the packet withthe highest Priority Index on for transmission. FIG. 2 illustrates thecase where the data packet at the head of the video queue 32 b has beendetermined to have the highest priority so that the distribution output39 is directing that packet 38 from the scheduler 30 for transmission.

With reference to FIG. 3, unclassified traffic, i.e. data packets thatare not classified according service requirements, arrives at atransmission scheduler component 40 of an AP. In this case, thescheduler preferably has a transmission queue that is structured withindividual queues that are each designated for data packets destined fora different STA. For this CoS unaware example, the memory device ispreferably configured with individual queues 42 a, 42 b, 42 c, . . . 42n to buffer data packets for each STA, STA_1, STA_2, STA_3, . . . STA_n,respectively, to which the AP is sending data. In the CoS unawarescenario, the queue structure is preferably continually adjusted toprovide for additional queues for STAs commencing data communicationsand eliminating queues for STAs that have terminated datacommunications. In FIG. 3, data packets are illustrated as appropriatelydistributed in each of the queues and marked with a number representingtheir respective destination STA.

Data packets arrive via a processing input 41 and are time stamped withan arrival time by a time stamping component 43 of the processingdevice. An input buffer 44 is preferably provided to the time stampingelement 43. A distribution element 45 of the processing device queueseach time stamped data packet into the tail of one of respectivepriority queues 42 a, 42 b, 42 c, . . . 42 n according to itsdestination. A data packet 46 destined for STA_1 is illustrated as beingqueued into the tail of the STA_1 queue 42 a by distribution element 45.

The scheduler 40 contains a calculating component 47 that calculates aPriority Index of each packet at the head of each queue 42 a, 42 b, 42c, . . . 42 n. A distribution output 49 of the scheduler 40, then sendsthe packet with the highest Priority Index on for transmission. FIG. 3illustrates the case where the data packet at the head of the STA_3queue 42 c has been determined to have the highest priority so that thedistribution output 49 is directing that packet 48 from the scheduler 40for transmission.

Preferably, the calculating component 37, 47 calculates the PriorityIndex for each data packet based in part on both data rate and waitingtime. A standard rate control algorithm is preferably used to determinethe data rate. Waiting time for each packet in the queue is preferablydetermined based on a current time value minus the stamped arrival time.

Two preferred variations of the calculations of the Priority Index areprovided by the following equations:PriorityIndex=[α×DataRateIndex]+[(1−α)×DelayIndex]orPriorityIndex=α×DataRateIndex×DelayIndexwhere: α is a weight factor to give higher priority to specific classes,

${{DataRateIndex} = \frac{CurrentTransmissionDataRate}{MaxDataRate}},{and}$${DelayIndex} = {\frac{WaitingTime}{T\;\max}.}$

The weight factor α can be set differently per priority queue to givehigher priority to one class or one STA over the other. The weightfactor α can be set to zero or a small number to achieve maximumcapacity. The weight factor α can be set to value bigger than 1 toachieve the best QoS performance.

CurrentTransmissionDataRate is the rate at which the AP is then using totransmit data. MaxDataRate is the maximum system specified rate, e.g.,for 802.11b, it is 11 Mbps as reflected in Table 1 above.

Tmax is a value for maximum allowed queuing. Tmax can be set perpriority queue in the case of the CoS aware scenario. For example, forthe queues 32 a-d illustrated in the example of FIG. 2, Tmax for thevoice queue 32 a is preferably set in a range of 5 to 10 ms; Tmax forthe video queue 32 b is preferably set in a range of 10 to 100 ms; Tmaxfor the interactive data queue 32 c is preferably set in a range of 100ms to 1 second; and Tmax for the low priority data queue 32 d ispreferably set in at a value greater than 1 second. In case of the CoSunaware scenario of FIG. 3, the AP preferably has one value for Tmax tolimit the maximum delay in the whole system.

In some cases, the AP may be dynamically configured to support differentsets of data rates at different times. In those instances, the queueallocation of a CoS aware scheduler may be dynamically adjusted inaccordance with the set of data rates which are currently in effect atthe AP. For example, a combined 802.11b/802.11g system may have APsconfigured to dynamically select between operating in a mode supportingonly the 802.11b data rates and a mode supporting the more inclusive setof 802.11g data rates. Preferably, the APs are capable of switchingbetween these two modes and advertising which rates are currentlysupported.

As can be seen from Tables 3 and 4, for rates of 12 Mpbs or lower, it ispossible to choose either an 802.11g rate or an 802.11b rate for thesame environment. The chosen rate is preferably selected to allowfairness between 802.11b and 802.11g devices and to maximize the usablethroughput. Fairness is of interest where there is an existing installedbase of 802.11b devices and it is desired that the introduction of802.11g does not noticeably degrade 802.11b performance.

The decision to use slower 802.11b rates over 802.11g rates in theinterest of fairness preferably is made to depend on the number of pure802.11b devices, the number of 802.11g devices, and the signal qualityof those devices. For example, if there are ten (10) 802.11g devices alloperating at or below 12 Mbps, and only one (1) 802.11b device, thechannel throughput gains exceed the performance degradations of the802.11b device. If there are devices operating and capable of 54 Mbpsperformance, it is not advantageous to force the system to operateexclusively in the 802.11b mode.

Tables 3 and 4 below show the rates for 802.11b and 802.11g, as well asthe usable throughput, and the time required to send a 1500 byte packet.

TABLE 3 802.11b Rate Characteristics Comparison. Example 802.11bReceiver Usable Time to send one Rate Modulation Sensitivity Throughput1500-byte packet (Mbps) Scheme (dBm) (Mbps) (microseconds) 11 8-bit −857.43 1615 CCK/DQPSK 5.5 4-bit −88 4.4 2731 CCK/DQPSK 2 DQPSK −91 1.86636 1 DBPSK −94 0.9 12828

TABLE 4 802.11g Rate Characteristics Comparison Usable Throughput Timeto send Usable (Combined one 1500 byte Example Throughput 802.11bpackets Receiver (802.11g and (Combined 802.11g Rate ModulationSensitivity only 802.11g system) (Mbps) Scheme (dBm) system) system)(microseconds) 54 64 QAM, 3/4 −71 36.4 19.9 603 48 64 QAM, 2/3 −72 33.519 632 36 16-QAM, 3/4 −76 27.1 16.7 717 24 16-QAM, 1/2 −80 19.6 13.5 88718 QPSK, 3/4 −83 15.3 11.3 1058 12 QPSK, 1/2 −85 10.7 8.6 1401 9 BPSK,3/4 −87 8.2 6.9 1744 6 BPSK, 1/2 −88 5.6 4.9 2430

With reference to Table 4, if the system has only 802.11g devices, theusable throughput is shown in the 4^(th) column. In the presence of any802.11b devices, the usable throughput drops and is shown in the 5^(th)column.

Based on the above examples of receiver sensitivities, and using a freeSpace Path loss model, an example of a throughput vs. range curve isshown in FIG. 4. It can be seen from FIG. 4 that the smaller thedistance between the receiver and transmitter, the higher the effectivethroughput. FIG. 4 also shows that the 802.11g rates provide a greaterthroughput for the same range as compared with 802.11b devices. Asillustrated, the throughputs converge as the distance approachesapproximately 250 meters. FIG. 4 represents an example in anoise-limited system. For a system with different receiversensitivities, the ranges would different.

FIG. 5 illustrates a system composed of an AP and two 802.11b clients,i.e., STAs, STA 1 and STA 2, and shows a data packet transmission ofeach STA reflecting equality of access. Each STA transmission (i.e., STA1 and STA 2) is followed by an acknowledge (ACK) frame from the AP.

FIG. 6 shows the same system as FIG. 5, but with one of the 802.11bdevices, STA 2, replaced by an 802.11g device. FIG. 6 illustrates a datapacket transmission of the STA reflecting inequality of access, the STA2 802.11g device having twice the access. Each STA transmission (i.e.,STA 1 and STA 2) is followed by an acknowledge (ACK) frame from the AP.The STA 2 transmissions are preceded by a clear to send (CTS) frame,which is required for co-existence.

The throughputs for STA 1 and STA 2 for the FIG. 5 when both STAs are802.11b stations operating at 11 Mbps example can be calculated asfollows:

$\begin{matrix}{{Throughput} = {\left( {{Data}\mspace{14mu}{sent}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)/\left( {{Time}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)}} \\{= {\left( {2*1500\mspace{14mu}{bytes}} \right)/\left( {2*1615\mspace{14mu}{microseconds}} \right)}} \\{= {7.4\mspace{14mu}{Mbps}\mspace{14mu}{channel}\mspace{14mu}{throughput}\mspace{14mu}\left( {{i.e.\mspace{14mu} 3.71}\mspace{14mu}{Mbps}} \right.}} \\{\left. {{for}\mspace{14mu}{each}\mspace{14mu}{STA}} \right).}\end{matrix}$

For the FIG. 6 example where STA 2 functions as an 802.11g deviceoperating at 12 Mbps, the throughput calculations are:

$\begin{matrix}{{Throughput} = {\left( {{Data}\mspace{14mu}{sent}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)/\left( {{Time}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)}} \\{= {\left( {1500 + {2*1500\mspace{14mu}{bytes}}} \right)/\left( {1615 + {2*1401}} \right.}} \\\left. {microseconds} \right) \\{= {8.15\mspace{14mu}{Mbps}\mspace{14mu}{channel}\mspace{14mu}{throughput}\mspace{14mu}\left( {{i.e.\mspace{14mu} 2.72}\mspace{14mu}{Mpbs}} \right.}} \\{{for}\mspace{14mu} 802.11b\mspace{14mu}{STA}\mspace{14mu} 1\mspace{14mu}{and}\mspace{14mu} 5.43\mspace{14mu}{Mbps}\mspace{14mu}{for}} \\{\left. {802.11g\mspace{14mu}{STA}\mspace{14mu} 2} \right).}\end{matrix}$As reflected in FIG. 6, the 802.11g device, STA 2 gets on average doublethe access opportunities. Although the channel throughput has increasedfrom 7.4 to 8.15 Mbps (10%), the throughput for the 802.11b device hasdecreased 27%.

Similarly, for two (2) 802.11b devices operating at 5.5 Mbps, thethroughput is:

$\begin{matrix}{{Throughput} = {\left( {{Data}\mspace{14mu}{sent}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)/\left( {{Time}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)}} \\{= {\left( {2*1500\mspace{14mu}{bytes}} \right)/\left( {2*2731\mspace{14mu}{microseconds}} \right)}} \\{= {4.4\mspace{14mu}{Mbps}\mspace{14mu}{channel}\mspace{14mu}{throughput}\mspace{14mu}\left( {{i.e.\mspace{11mu} 2.2}\mspace{14mu}{Mbps}} \right.}} \\{\left. {{for}\mspace{14mu}{each}\mspace{14mu}{STA}} \right).}\end{matrix}$

Comparatively, for one 802.11b device operating at 5.5 Mbps, and one802.11g device operating at 6 Mbps, the throughput is:

$\begin{matrix}{{Throughput} = {\left( {{Data}\mspace{14mu}{sent}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)/\left( {{Time}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)}} \\{= {{\left( {1500 + {2*1500\mspace{14mu}{bytes}}} \right)/2731} + {2*2430}}} \\\left. {microseconds} \right) \\{= {4.8\mspace{14mu}{Mbps}\mspace{14mu}{channel}\mspace{14mu}{throughput}\mspace{14mu}\left( {{i.e.\mspace{14mu} 1.6}\mspace{14mu}{Mbps}\mspace{14mu}{for}} \right.}} \\{\left. {802.11b\mspace{14mu}{STA}\mspace{14mu} 1\mspace{14mu}{and}\mspace{14mu} 3.2\mspace{14mu}{Mbps}\mspace{14mu}{for}\mspace{14mu} 802.11g\mspace{14mu}{STA}\mspace{14mu} 2} \right).}\end{matrix}$In this latter comparison, the channel throughput increase is from 4.4to 4.8 Mbps (9%), but the drop in throughput for the 802.11b device is27%.

In these two comparisons, it is seen that while there is an increase inthe channel throughput when the 802.11g mode is used for STA 2 asopposed to the 802.11b mode, there is a substantial decrease in theperformance of the 802.11b device.

A further comparative example illustrates the lack of fairness when thechannel quality is extremely poor, e.g. due to high interference, suchthat the 1 Mbps rate is chosen. Normally, as long as an AP advertisesthat it supports 802.11g rates, the 802.11g devices use a smallercontention window, even when operating at 802.11b rates.

For two (2) 802.11b devices, one operating at 11 Mbps, and the other at1 Mbps, the throughput is:

$\begin{matrix}{{Throughput} = {\left( {{Data}\mspace{14mu}{sent}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)/\left( {{Time}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)}} \\{= {\left( {2*1500\mspace{14mu}{bytes}} \right)/\left( {1615 + {12828\mspace{14mu}{microseconds}}} \right)}} \\{= {1.66\mspace{14mu}{Mbps}\mspace{14mu}{channel}\mspace{14mu}{throughput}\mspace{14mu}\left( {{i.e.\mspace{14mu} 0.83}\mspace{14mu}{Mbps}} \right.}} \\{\left. {{for}\mspace{14mu}{each}\mspace{14mu}{STA}} \right).}\end{matrix}$

Comparatively, for one 802.11b device operating at 11 Mbps, and one802.11g device operating at 1 Mbps, the throughput is:

$\begin{matrix}{{Throughput} = {\left( {{Data}\mspace{14mu}{sent}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)/\left( {{Time}\mspace{14mu}{per}\mspace{14mu}{cycle}} \right)}} \\{= {\left( {1500 + {2*1500\mspace{14mu}{bytes}}} \right)/\left( {1615 + {2*12828}} \right.}} \\\left. {microseconds} \right) \\{= {1.32\mspace{14mu}{Mbps}\mspace{14mu}{channel}\mspace{14mu}{throughput}\mspace{11mu}\left( {{i.e.\mspace{14mu} 0.44}\mspace{14mu}{Mbps}\mspace{14mu}{for}} \right.}} \\{\left. {802.11b\mspace{14mu}{STA}\mspace{14mu} 1\mspace{14mu}{and}\mspace{14mu} 0.89\mspace{14mu}{Mbps}\mspace{14mu}{for}\mspace{14mu} 802.11g\mspace{14mu}{STA}\mspace{14mu} 2} \right).}\end{matrix}$

In this third comparison, the 802.11b device throughput decreases by53%, and additionally, there is a decrease in the channel throughput dueto the slower 802.11g device occupying the channel for longer periods.

FIG. 7 illustrates a procedure that can be implemented by an APprocessor to determine what rates are advertised via the AP'stransmitter. Generally, when a system has devices that are all 802.11gor where the frame error rate (FER) is below a given threshold, then allrates are supported. When the system has only 802.11b devices, it isstill of interest to advertise support of 802.11g rates, in the casethat an 802.11g device begins to operate at a high rate (i.e., at a rateabove the range of 802.11b devices). When the frame error rate (FER) isbelow a given threshold which indicates that the channel quality isgood, and 802.11g devices should not be restricted from using higherrates, if possible.

For the preferred process shown in FIG. 7, at step S1 the process isstarted when a change in the number of STAs or in the FER is detected.At step S2 variables m and n are assigned the number of 802.11b and802.11g STAs, respectively, that are communicating with the AP. At stepS3, a determination is made if all STAs are 802.11g, i.e. no 802.11bSTAs, m=0, or if FER is below a selected threshold High_Thres. If eitheris the case, at step S4, all rates are supported and the process ends,step S5.

If not, a determination is made at step S6 whether the system has any802.11g devices using rates above 12 Mbps. If not, then both 802.11g and802.11b device rates are supported, step S4. When 802.11b devices arepresent, and all 802.11g devices are operating at or below 12 Mbps, S6,(e.g., due to a high interference environment), the decision aboutwhether to eliminate support of the 802.11g mode is determined byascertaining the relative number of 802.11b devices (in) and 802.11gdevices (n) in steps S7, S8. The ratio is calculated in step S7 and adetermination is made in step S8. When m/n is less than a giventhreshold, 802.11g rates are disabled are in step S9 and the processends step S10. When the ratio of 802.11b devices to 802.11g devices(m/n) is greater than the threshold, both the 802.11g and the 802.11brates are supported, step S4.

This method is particularly applicable in situations where the highmodulation rates would not be used, e.g. in a system where interferenceis high, or where all devices are located at large distances from theAP.

The preferred measures taken to ensure backward compatibility toexisting 802.11b devices with the introduction of 802.11g devicesinclude:

-   -   In the presence of any 802.11b client devices (STA), prior to        any transmission, all 802.11g devices inform the 802.11b devices        of the impending transmission. This is accomplished by        transmitting a Clear-to-send frame (CTS-to-self). The effect of        this additional CTS frame is a reduction in effective throughput        for 802.11g (see Table 4, columns 4 and 5).    -   In terms of access to the radio channel, all existing 802.11        systems preferably use a random backoff timer in order to        determine when to attempt a transmission. The choice of the        random number is preferably between [0,31] for 802.11b, and        [0,15] for 802.11g. The reason for the difference in the range        of the backoff values for 802.11b and 802.11g systems is to give        802.11g devices, which presumably operate at a higher rate, a        higher probability of accessing the channel, so that the channel        is used more efficiently. The effect of this is that 802.11g        devices typically get twice the transmission opportunities of        802.11b devices. As long as the AP advertises that it supports        the 802.11g rates, the 802.11g devices will always use the        smaller contention window, even when operating at an 802.11b        rate.

Preferably, the components the WTRU's scheduler are implemented on ansingle integrated circuit, such as an application specific integratedcircuit (ASIC). Similarly, the receiving unit, the signal processingunit and the transmitting unit of a rate advertising WTRU can beimplemented on an ASIC. However, in either case, the components may alsobe readily implemented on multiple separate integrated circuits.

The foregoing description makes references to 802.11 type systems as anexample only and not as a limitation. Other variations and modificationsconsistent with the invention will be recognized by those of ordinaryskill in the art.

1. A wireless transmit/receive unit (WTRU) for conducting wirelesscommunications with a plurality of other WTRUs that implements a processfor controlling transmission of wireless communication data to the otherWTRUs comprising: a scheduler configured to queue data packets fortransmission to other WTRUs based on a transmission rate of the packetsand to selectively enable transmission of queued data packets fromtransmission rate assigned queues in successive turns based on anallocated time period for each queue turn such that a shortest timeperiod is allocated for data packets queued in a lowest transmissionrate queue and a longest time period is allocated for data packetsqueued in a highest transmission rate queue.
 2. The WTRU of claim 1wherein the scheduler is configured to allocate a time period for agiven queue that is at least as long as the time period allocated foreach queue assigned for data packets designated for transmission at alower transmission rate than the transmission rate assigned to the givenqueue.
 3. The WTRU of claim 1 configured as an Access Point (AP) for a802.11 wireless local area network (WLAN).
 4. The WTRU of claim 1wherein the scheduler is implemented in an application specificintegrated circuit (ASIC).
 5. A wireless transmit/receive unit (WTRU)for conducting wireless communications with a plurality of other WTRUsthat implements a process for controlling communication of wirelesscommunication data with the other WTRUs comprising: a schedulerconfigured to selectively enable communication of data packets withother WTRUs in successive turns based on an allocated time period foreach turn such that a shortest time period is allocated for data packetscommunicated at a lowest transmission rate and a longest time period isallocated for data packets communicated at a highest transmission rate.6. The WTRU of claim 5 wherein the scheduler is configured to allocatetime periods for receiving data packets from other WTRUs such that eachother WTRU is provided a transmission time for its respective turn basedupon the transmission rate at which that WTRU is to transmit datapackets that is at least as long as the time period allocated for datapackets designated for transmission at a lower transmission rate thanthe transmission rate at which that WTRU is to transmit data packets. 7.The WTRU of claim 6 wherein the scheduler is configured to queue datapackets for transmission to other WTRUs based on transmission rate andto selectively enable transmission of queued data packets fromtransmission rate assigned queues in successive turns based on anallocated time period for each queue turn such that a shortest timeperiod is allocated for data packets queued in a lowest transmissionrate queue and a longest time period is allocated for data packetsqueued in a highest transmission rate queue.
 8. The WTRU of claim 7wherein the scheduler is configured to allocate a time period for agiven queue that is at least as tong as the time period allocated foreach queue assigned for data packets designated for transmission at alower transmission rate than the transmission rate assigned to the givenqueue.
 9. The WTRU of claim 8 configured as an Access Point (AP) for a802.11 wireless local area network (WLAN).
 10. The WTRU of claim 8wherein the scheduler is implemented in an application specificintegrated circuit (ASIC).
 11. A method for conducting wirelesscommunication of data between a wireless transmit/receive unit (WTRU)and a plurality of other WTRUs and for controlling transmission of suchdata to the other WTRUs comprising: queuing data packets fortransmission to other WTRUs based on transmission rate wherein there aremultiple queues, each queue holding packets for transmission at a singletransmission rate; and selectively enabling transmission of queued datapackets from transmission rate assigned queues in successive turns basedon an allocated time period for each queue turn such that a shortesttime period is allocated for data packets queued in a lowesttransmission rate queue and a longest time period is allocated for datapackets queued in a highest transmission rate queue.
 12. The method ofclaim 11 wherein a time period is allocated for a given queue that is atleast as long as the time period allocated for each queue assigned fordata packets designated for transmission at a lower transmission ratethan the transmission rate assigned to the given queue.
 13. The methodof claim 11 wherein the method is conducted by a WTRU configured as anAccess Point (AP) for a 802.11 wireless local area network (WLAN).
 14. Amethod for conducting wireless data communication between a wirelesstransmit/receive unit (WTRU) and a plurality of other WTRUs thatimplements a process for controlling data communication with the otherWTRUs comprising: selectively enabling communication of data packetswith other WTRUs in successive turns based on an allocated time periodfor each turn such that a shortest time period is allocated for datapackets communicated at a lowest transmission rate and a longest timeperiod is allocated for data packets communicated at a highesttransmission rate.
 15. The method of claim 14 wherein time periods areallocated for receiving data packets from other WTRUs such that eachother WTRU is provided a transmission time for its respective turn basedupon the transmission rate at which that WTRU is to transmit datapackets that is at least as long as the time period allocated for datapackets designated for transmission at a lower transmission rate thanthe transmission rate at which that WTRU is to transmit data packets.16. The method of claim 15 wherein data packets are queued fortransmission to other WTRUs based on transmission rate and transmissionof queued data packets is selectively enabled from transmission rateassigned queues in successive turns based on an allocated time periodfor each queue turn such that a shortest time period is allocated fordata packets queued in a lowest transmission rate queue and a longesttime period is allocated for data packets queued in a highesttransmission rate queue.
 17. The method of claim 16 wherein a timeperiod is allocated for a given queue that is at least as long as thetime period allocated for each queue assigned for data packetsdesignated for transmission at a lower transmission rate than thetransmission rate assigned to the given queue.
 18. The method of claim17 wherein the method is conducted by a WTRU configured as an AccessPoint (AP) for a 802.11 wireless local area network (WLAN).